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Biomedical subjects

M Lichtwarck-Aschoff

Publications and source records attributed to M Lichtwarck-Aschoff.

29 records · Page 2Linked to original sources
PubMed1996

Oxygenation remains unaffected by increased inspiration-to-expiration ratio but impairs hemodynamics in surfactant-depleted piglets.

OBJECTIVES: Prolongation of inspiratory time is used to reduce lung injury in mechanical ventilation. The aim of this study was to isolate the effects of inspiratory time on airway pressure, gas exchange, and hemodynamics, while ventilatory frequency, tidal volume, and mean airway pressure were kept constant. DESIGN: Randomized experimental trial. SETTING: Experimental laboratory of a University Department of Anesthesiology and Intensive Care. ANIMALS: Twelve anesthetised piglets. INTERVENTIONS: After lavage the reference setting was pressure-controlled ventilation with a decelerating flow; I:E was 1:1, and PEEP was set to 75% of the inflection point pressure level. The I:E ratios of 1.5:1, 2.3:1, and 4:1 were applied randomly. Under open lung conditions, mean airway pressure was kept constant by reduction of external PEEP. MEASUREMENTS AND RESULTS: Gas exchange, airway pressures, hemodynamics, functional residual capacity (SF6 tracer), and intrathoracic fluid volumes (double indicator dilution) were measured. Compared to the I:E of 1:1, PaCO2 was 8% lower, with I:E 2.3:1 and 4:1 (p < or = 0.01) while PaO2 remained unchanged. The decrease in inspiratory airway pressure with increased inspiratory time was due to the response of the pressure-regulated volume-controlled mode to an increased I:E ratio. Stroke index and right ventricular ejection fraction were depressed at higher I:E ratios (SI by 18% at 2.3:1, 20% at 4:1; RVEF by 10% at 2.3:1, 13% at 4:1; p < or = 0.05). CONCLUSION: Under open lung conditions with an increased I:E ratio, oxygenation remained unaffected while hemodynamics were impaired.

Animals↗
PubMed1996

Central venous pressure, pulmonary artery occlusion pressure, intrathoracic blood volume, and right ventricular end-diastolic volume as indicators of cardiac preload.

PURPOSE: Central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP) and right ventricular end-diastolic volume (RVEDV) are often regarded as indicators of both circulating blood volume and cardiac preload. to evaluate these relationships, the response of each variable to induced volume shifts was tested. The relationships between these variables and cardiac index (CI) and stroke volume index (SVI) was also recorded to assess the utility of each variable as an indicator of cardiac preload. The responses of the new variable intrathoracic blood volume (ITBV) to the same maneuvers was also tested. To examine the effects of changes in cardiac output alone on ITBV, the effects of infusing dobutamine were studied. MATERIALS AND METHODS: Ten anesthetized piglets were studied during conditions of normovolemia, hypovolemia, and hypervolemia. The effects of an infusion of dobutamine were examined under normovolemia and hypovolemia. Cardiac output was measured by thermo-dilution, and ITBV was measured by double-indicator dilution. RESULTS: CI was correlated to CVP with r2 = .42 (P < or = .01), to PAOP with r2 = .43 (P < or = .01), to RVEDV index with r2 = .21 (P < or = .01), and to ITBV with r2 = .78 (P < or = .01) (pooled absolute values). Bias (mean difference of the percent changes with normovolemia = 100%) +/- 1 SD; for SVI - ITBV index was 1 +/- 22%, for SVI - CVP it was -128 +/- 214%; for SVI - PAOP it was -36 +/- 46%; and for SVI - RVEDV index it was 1 +/- 29%. Dobutamine infusion increased heart rate (to about 190 x min-1 and CI by 30% in normovolemia and hypovolemia, while ITBV remained basically unchanged. CONCLUSIONS: Under the experimental conditions chosen neither CVP, PAOP, nor RVEDV reliably indicated changes in circulating blood volume, nor were they linearly and tightly correlated to the resulting changes in SVI. ITBV reflected both changes in volume status and the resulting alteration in cardiac output. The possibility that ITBV might be cardiac output-dependent was not supported. ITBV, therefore, shows potential as a clinically useful indicator of overall cardiac preload.

Analysis of Variance↗
PubMed1996

Ventilation with constant versus decelerating inspiratory flow in experimentally induced acute respiratory failure.

BACKGROUND: Recognition of the potential for ventilator-associated lung injury has renewed the debate on the importance of the inspiratory flow pattern. The aim of this study was to determine whether a ventilatory pattern with decelerating inspiratory flow, with the major part of the tidal volume delivered early, would increase functional residual capacity at unchanged (or even reduced) inspiratory airway pressures and improve gas exchange at different positive end-expiratory pressure levels. METHODS: Surfactant depletion was induced by repeated bronchoalveolar lavage in 13 anesthetized piglets. Decelerating and constant inspiratory flow ventilation was applied at positive end-expiratory pressure levels of 22, 17, 13, 9, and 4 cm H(2)O. Tidal volume, inspiration-to-expiration ratio, and ventilatory frequency were kept constant. Airway pressures, gas exchange, functional residual capacity (using a wash-in/washout method with sulfurhexafluoride), central hemodynamics, and extravascular lung water (using the thermo-dye-indicator dilution technique) were measured. RESULTS: Decelerating inspiratory flow yielded a lower arterial carbon dioxide tension compared to constant flow, that is, it improved alveolar ventilation. There were no differences between the flow patterns regarding end-inspiratory occlusion airway pressure, end-inspiratory lung volume, static compliance, or arterial oxygen tension. No differences were seen in hemodynamics and oxygen delivery. CONCLUSIONS: The decelerating inspiratory flow pattern increased carbon dioxide elimination, without any reduction of inspiratory airway pressure or apparent improvement in arterial oxygen tension. It remains to be established whether these differences are sufficiently pronounced to justify therapeutic consideration.

Acute Disease↗
PubMed1996

Under open lung conditions inverse ratio ventilation causes intrinsic PEEP and hemodynamic impairment.

Inverse ratio ventilation (IRV) is commonly used in clinical practice. Several studies have used IRV in order to recruit collapsed alveoli. In a randomised trial in twelve surfactant depleted piglets, the lungs were ventilated with sufficient positive end-expiratory pressure (PEEP) to prevent end-expiratory collapse, and the effects of increased inspiration-to-expiration (I:E ratio) were evaluated. Pressure regulated ventilation (with I:E of 1:1, constant tidal volume and decelerating inspiratory flow) was used at 30 breaths per minute (bpm). I:E ratios of 1.5:1, 2.3:1 and 4:1 were applied sequentially. When the I:E ratio was increased, external PEEP had to be reduced in order to keep total PEEP constant. Functional residual capacity, airway pressures, gas exchange, extrathermal volume and hemodynamics were measured. With I:E ratios above 2:1 intrinsic PEEP was generated and with concomitant decrease in cardiac index. PaO2 was not affected, but oxygen delivery was reduced. It is concluded that I:E ratios of 2:1, or above, generate increased intrinsic PEEP with compromised hemodynamics.

Animals↗
PubMed1995

Different ventilatory approaches to keep the lung open.

OBJECTIVES: To study the ability of different ventilatory approaches to keep the lung open. DESIGN: Different ventilatory patterns were applied in surfactant deficient lungs with PEEP set to achieve pre-lavage PaO2. SETTING: Experimental laboratory of a University Department of Anaesthesiology and Intensive Care. ANIMALS: 15 anaesthetised piglets. INTERVENTIONS: One volume-controlled mode (L-IPPV201:1.5) and two pressure-controlled modes at 20 breaths per minute (bpm) and I:E ratios of 2:1 and 1.5:1 (L-PRVC202:1 and L-PRVC201.5:1), and two pressure-controlled modes at 60 bpm and I:E of 1:1 and 1:1.5 (L-PRVC601:1 and L-PRVC601:1.5) were investigated. The pressure-controlled modes were applied using "Pressure-Regulated Volume-Controlled Ventilation" (PRVC). MEASUREMENTS AND RESULTS: Gas exchange, airway pressures, hemodynamics, FRC and intrathoracic fluid volumes were measured. Gas exchange was the same for all modes. FRC was 30% higher with all post-lavage settings. By reducing inspiratory time MPAW decreased from 25 cmH2O by 3 cmH2O with L-PRVC201.5:1 and L-PRVC601:1.5. End-inspiratory airway pressure was 29 cmH2O with L-PRVC201.5:1 and 40 cmH2O with L-IPPV201:1.5, while the other modes displayed intermediate values. End-inspiratory lung volume was 65 ml/kg with L-IPPV201:1.5, but it was reduced to 50 and 49 ml/kg with L-PRVC601:1 and L-PRVC601:1.5. Compliance was 16 and 18 ml/cmH2O with L-PRVC202:1 and L-PRVC201.5:1, while it was lower with L-IPPV201:1.5, L-PRVC601:1 and L-PRVC601:1.5. Oxygen delivery was maintained at pre-lavage level with L-PRVC201.5:1 (657 ml/min.m2), the other modes displayed reduced oxygen delivery compared with pre-lavage. CONCLUSION: Neither the rapid frequency modes nor the low frequency volume-controlled mode kept the surfactant deficient lungs open. Pressure-controlled inverse ratio ventilation (20 bpm) kept the lungs open at reduced end-inspiratory airway pressures and hence reduced risk of barotrauma. Reducing I:E ratio in this latter modality from 2:1 to 1.5:1 further improved oxygen delivery.

Analysis of Variance↗
PubMed1995

Accuracy and reproducibility of the measurement of actively circulating blood volume with an integrated fiberoptic monitoring system.

OBJECTIVE: Bedside monitoring of circulating blood volume has become possible with the introduction of an integrated fiberoptic monitoring system that calculates blood volume from the changes in blood concentration of indocyanine green dye 4 mins after injection. The aim of this investigation was to compare the blood volume estimate of the integrated fiberoptic monitoring system (group 1) with the standard methods of blood volume measurement using Evans blue (group 2), and indocyanine green measured photometrically (group 3). DESIGN: Prospective laboratory study. SETTING: Animal laboratory of a University's institute for experimental surgery. SUBJECTS: Eleven anesthetized, paralyzed, and mechanically ventilated piglets. INTERVENTIONS: A central venous catheter was used for the injection of the indicator dyes (Evans blue and indocyanine green). A fiberoptic thermistor catheter was advanced into the thoracic aorta. The fiberoptic catheter detects indocyanine green by reflection densitometry for the estimation of blood volume of the integrated fiberoptic monitoring system. Samples for the determination of Evans blue and indocyanine green concentrations were drawn from an arterial catheter in the femoral artery over a period of 17 mins after injection. MEASUREMENTS AND MAIN RESULTS: Measurements were performed during normovolemia, hypovolemia (blood withdrawal of < or = 30 mL/kg), and hypervolemia (retransfusion of the withdrawn blood plus an infusion of 10% hydroxyethyl starch [45 mL/kg]). Linear regression, correlation, and bias were calculated for the comparison of the blood volume estimates by the fiberoptic monitoring system (group 1) vs. the total blood volume estimates using Evans blue (group 2) and indocyanine green (group 3): group 1 = 0.82.group 2-26 mL; r2 = 82.71%; r = .91; n = 40; group 1-group 2 +/- 1 SD = -435 +/- 368 mL; group 1 = 0.79.group 3 + 50 mL; r2 = 74.81%; r = .87; n = 28; group 1-group 3 +/- 1 SD = -506 +/- 374 mL. CONCLUSIONS: The results demonstrate that the blood volume estimate of the fiberoptic monitoring system (group 1) correlates closely with the total blood volume measurement using Evans blue (group 2) and indocyanine green (group 3). Trapped indicator in the packed red cell column after centrifugation of the blood samples may account for an overestimation of group 2 and group 3 of approximately 10% to 14%, but there still remains a proportional difference of 10% between group 1 vs. group 2 and vs. group 3. This difference is due to the longer mixing times of group 3 (16 mins) and group 2 (17 mins), during which they are distributed in slowly exchanging blood pools. It seems that the blood volume estimate of the fiberoptic monitoring system (group 1) represents the actively circulating blood volume and may be useful for bedside monitoring.

Animals↗
PubMed1994

Monitoring of right ventricular function using a conventional slow response thermistor catheter.

OBJECTIVE: To investigate whether determination of right ventricular end-diastolic volume (RVEDV) and right ventricular ejection fraction (RVEF) can be performed with reasonable accuracy and reproducibility using a conventional slow response thermistor pulmonary artery catheter (CPAC) applying an adaptive algorithm. DESIGN: To study RVEDV and RVEF simultaneously with pulmonary artery catheters equipped with slow and fast response thermistors (FRPAC) under a broad range of cardiac output. SETTING: Laboratory of Institute of Experimental Surgery, Technical University. ANIMALS: 11 anaesthetised piglets. INTERVENTIONS: Hypovolemia (V-) was induced by withdrawal of blood up to 50 ml/kg, hypervolemia (V+) was produced by retransfusing blood and adding up to 30 mg/kg hydroxyethyl starch. In 5 animals in phases V- and V+ beta-adrenergic stimulation was achieved with dobutamine. Finally pulmonary artery hypertension was induced by infusion of small air bubbles. MEASUREMENTS AND RESULTS: Cardiac output (CO), RVEDV and RVEF were determined simultaneously with FRPAC and CPAC placed in the same pulmonary artery branch. Measurements were repeated 8 times sequentially in steady state normovolemia. A total of 130 measurements could be analysed. The coefficient of variation was 6.7 +/- 4.2% for CO(FRPAC) and 4.6 +/- 1.7% for CO(CPAC); for RVEF it was 9.7 +/- 6.2% (FRPAC) and 9.9 +/- 3.9% (CPAC); for RVEDV it was 11.6 +/- 4.8% (FRPAC) and 8.54 +/- 3.2 (CPAC). Mean difference (bias) was 0.06 +/- 0.39 l/min for CO measured with both methods, 19 +/- 35 ml for RVEDV and -3.3 +/- 6.5% for RVEF. CO(CPAC) displayed a strong correlation to CO(FRPAC) (R = 0.97, p = 0.001) as well as RVEF (R for RVEF(CPAC) versus RVEF(FRPAC) = 0.90, p = 0.001). R for RVEDV(CPAC) versus RVEDV(FRPAC) was 0.67, p = 0.001. We conclude that this animal study demonstrates good agreement between RVEF and RVEDV obtained with catheters equipped with a fast response thermistor or with a conventional slow response thermistor allowing accurate monitoring of right ventricular function with a conventional pulmonary artery catheter.

Algorithms↗
PubMed1992

An experimental randomized study of five different ventilatory modes in a piglet model of severe respiratory distress.

OBJECTIVES: To characterize different modes of pressure- or volume-controlled mechanical ventilation with respect to their short-term effects on oxygen delivery (DO2). Furthermore to investigate whether such differences are caused by differences in pulmonary gas exchange or by airway-pressure-mediated effects on the central hemodynamics. DESIGN: After inducing severe respiratory distress in piglets by removing surfactant, 5 ventilatory modes were randomly and sequentially applied to each animal. SETTING: Experimental laboratory of a university department of Anesthesiology and Intensive Care. ANIMALS: 15 piglets after repeated bronchoalveolar lavage. INTERVENTIONS: Volume-controlled intermittent positive-pressure ventilation (IPPV) with either 8 or 15 cmH2O PEEP; pressure-controlled inverse ratio ventilation (IRV); pressure-controlled high-frequency positive-pressure ventilation (HFPPV) and pressure-controlled high frequency ventilation with inspiratory pulses superimposed (combined high frequency ventilation, CHFV). The prefix (L) indicates that lavage has been performed. MEASUREMENTS AND RESULTS: Measurements of gas exchange, airway pressures, hemodynamics, functional residual capacity (using the SF6 method), intrathoracic fluid volumes (using a double-indicator dilution technique) and metabolism were performed during ventilatory and hemodynamic steady state. The peak inspiratory pressures (PIP) were significantly higher in the volume-controlled low frequency modes (43 cmH2O for L-IPPV-8 and L-IPPV-15) than in the pressure-controlled modes (39 cmH2O for L-IRV, 35 cmH2O for L-HFPPV and 33 cmH2O for L-CHFV, with PIP in the high-frequency modes being significantly lower than in inverse ratio ventilation). The mean airway pressure (MPAW) after lavage was highest with L-IRV (26 cmH2O). In the ventilatory modes with a PEEP > 8 cmH2O PaO2 did not differ significantly and beyond this "opening threshold" MPAW did not further improve PaO2. Central hemodynamics were depressed by increasing airway pressures. This is especially true for L-IRV in which we found the highest MPAW and at the same time the lowest stroke index (74% of IPPV). CONCLUSIONS: In this model, as far as oxygenation is concerned, it does not matter in which specific way the airway pressures are produced. As far as oxygen transport is concerned, i.e. aiming at increasing DO2, we conclude that optimizing the circulatory status must take into account the circulatory influence of different modes of positive pressure ventilation.

Airway Resistance↗
PubMed1992

Intrathoracic blood volume accurately reflects circulatory volume status in critically ill patients with mechanical ventilation.

Positive pressure ventilation in patients with acute respiratory failure (ARF) may render the interpretation of central venous pressure (CVP) or pulmonary wedge pressure (PCWP) difficult as indicators of circulating volume. The preload component of cardiac (CI) and stroke index (SI) is also influenced by the increased intrathoracic pressures of positive pressure ventilation. Moreover CI and SI do not indicate volume status exclusively but also contractility and afterload. We investigated whether intrathoracic blood volume (ITBV) more accurately reflects blood volume status and the resulting oxygen transport (DO2). CVP, PCWP, cardiac (CI) and stroke index (SI) were measured, oxygen transport index (DO2I) and oxygen consumption index (VO2I) were calculated in 21 ARF-patients. Ventilatory patterns were adjusted as necessary. CI, SI and intrathoracic blood volume index (ITBVI) were derived from thermal dye dilution curves which were detected with a 5 F fiberoptic thermistor femoral artery catheter and fed into a thermal-dye-computer. All data were collected in intervals of 6 h. There were 224 data sets obtained. Linear regression analysis was performed between absolute values as well as between the 6 changes (prefix delta).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

An experimental study of different ventilatory modes in piglets in severe respiratory distress induced by surfactant depletion.

In 19 anesthetized piglets 3 ventilatory modes were studied after inducing pulmonary insufficiency by bronchoalveolar lavage by the method of Lachmann. The lavage model was considered suitable for reproduction of severe respiratory distress. This model was reproducible and stable with respect to alveolar collapse, decrease in static chest-lung compliance and increase in extravascular lung water. The ventilatory modes studied were volume-controlled intermittent positive-pressure ventilation (IPPV), pressure-controlled inverse ratio ventilation (IRV), and pressure-controlled high-frequency positive-pressure ventilation (HFPPV). The 3 ventilatory modes were used in random sequence for at least 30 min to produce a ventilatory steady state. Ventilation with no PEEP, permitting alveolar collapse, was interposed between each experimental mode. The ability to open collapsed alveoli, i.e. alveolar recruitment, was different. The recruitment rate for IPPV was 74%, but for IRV and HFPPV it was 95%, respectively. Although IRV provided the best PaO2, this was at the expense of high airway pressures with circulatory interference and reduced oxygen transport. In contrast to this, HFPPV provided lower airway pressures, less circulatory interference and improved oxygen transport. In the clinical setting there might be negative effects on vital organs and functions unless the ventilatory modes are continuously and cautiously adapted to the individual requirements in different phases of severe respiratory distress. Therefore, one ventilatory strategy could be to "open the airways" with IRV, but then switch to HFPPV in an attempt to maintain the airways open with lesser risk of barotrauma and with improved oxygen transport.

Animals↗